Re: What are requirements for allocator destructor?
On 18 Jul., 22:29, Zeljko Vrba <mordor.nos...@fly.srk.fer.hr> wrote:
In Dinkumware's reference, I found the following example:
===
For example, given an allocator object al of type A, you can allocate an object
of type Other with the expression:
A::rebind<Other>::other(al).allocate(1, (Other *)0)
===
I have written a pooled memory allocator that satisfies the std::allocator
interface. The destructor of my allocator releases the complete pool of
memory that it was managing, which makes the above example invalid - the
returned pointer becomes invalidated as soon as the temporary allocator
object gets destructed. On the other hand, the standard says nothing about
the expected behavior of the allocator's destructor.
What is this group's opinion on what the allocator's destructor should / is
allowed to do?
Is an instance of some_allocator<T> meant to persist through the whole
run-time of the program? Or is a program obliged to ensure that the
lifetime of the allocator exceeds the lifetime of the objects returned
by it?
There does not exist such a general whole-run-time requirement.
Allocators are supposed to be EqualityComparable and the meaning
of two allocator objects being equal is, that one can deallocate
memory allocated by the other one.
Unfortunately this basically good idea was near to worthless in
C++03, because a second normative wording also said that
implementations of containers are permitted to assume that all
instances of an allocator of a given type are interchangeable
and thus must be equal to each other.
This relaxation of the rules has been removed as of C++0x and
implementations are now required to honor equality of allocator
objects.
In both C++03 and C++0x the so-called default allocator of type
std::allocator guarantees that two objects std::allocator<T> and
std::allocator<U> with T potentially different from U always
returns true for operator==.
HTH & Greetings from Bremen,
Daniel Kr?gler
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